Resonant frequency, \({ f }=\frac { 1 }{ 2\pi \sqrt { LC } } \)
On simplifying, we get C = \(\frac { 1 }{ { 4\pi }^{ 2 }{ { f }^{ 2 } }L } \)
i) When frequency = 500 kHz,
\(C=\frac { 1 }{ 4\times { 3.14 }^{ 2 }\times { (500\times { 10 }^{ 3 }) }^{ 2 }\times 150\times { 10 }^{ -6 } } \)
= 676 pF
ii) When frequency = 1500 kHz,
\(C=\frac { 1 }{ 4\times { 3.14 }^{ 2 }\times { (1500\times { 10 }^{ 3 }) }^{ 2 }\times 150\times { 10 }^{ -6 } } \)
= 75 pF
Therefore, the capacitor range is 75 to 676 pF.

When V_CE = 15 V, I_C = 1.5 μA
When V_CE is changed to 10 V, I_C = 1.4 μA

\(\mathrm{V}_{\mathrm{cc}}=12 \mathrm{~V}, \mathrm{R}_{\mathrm{B}}=10 \mathrm{k} \Omega, \mathrm{R}_{\mathrm{E}}=1 \mathrm{k} \Omega, \mathrm{R}_{\mathrm{c}}=1+1=2 \mathrm{k} \Omega, \alpha=0.99, \mathrm{~V}_{\mathrm{BE}}=0.7 \mathrm{~V}, \mathrm{I}_{\mathrm{c}}=?\)
\(\beta=\alpha /(1-\alpha)=0.99 /(1-0.99)=99\)
\(\mathrm{I}_{\mathrm{B}}=\mathrm{I}_{\mathrm{C}} / \beta=\mathrm{I}_{\mathrm{c}} / 99\)
Applying Kirchoff's Voltage law,
\(I_C R_C+I_n R_n+I_E R_E+V_{u t}=V\)
\(2 \times 10^3 \mathrm{I}_{\mathrm{C}}+10 \times 10^3\left(\mathrm{I}_{\mathrm{C}} / 99\right)+1 \times 10^3\left(\mathrm{I}_{\mathrm{C}}+\mathrm{I}_{\mathrm{C}} / 99\right)+0.7=12 \quad\left(\because \mathrm{I}_{\mathrm{E}}=\mathrm{I}_{\mathrm{n}}+\mathrm{I}_{\mathrm{C}}\right)\)
\(\therefore \mathrm{I}_{\mathrm{C}}=\frac{11.3 \times 10^{-3} \times 99}{298}\)
\(\mathrm{I}_{\mathrm{C}}=3.7 \times 10^{-3} \mathrm{~A}=3.7 \mathrm{~mA}\)

Photo diode:
A p -n junction diode which converts an optical signal into electrical current is known as photodiode.
(i) The operation of photodiode is exactly inverse to that of an LED. Photodiode works in reverse bias condition.

(ii) The direction of arrows indicates that the light is incident on the photo diode.
(iii) The device consists of a p-n junction semiconductor made of photosensitive material kept safely inside a plastic case as shown in fig.
(iv) It has a small transparent window that allows light to be incident on the p-n junction.
(v) Photodiodes car generate current when the p - n junction is exposed to light and hence are called as light sensors.
(vi) When a photon of sufficient energy (hv) strikes the depletion region of the diode, some of the valence band electron are elevated into conduction band, in turn holes are developed in the valence band. This creates electron-hole pairs. The amount of electron - hole pairs generated depends on the intensity of light incident on the p - n junction.
(vii) These electron and holes are swept across the p-n junction by the electric field created by reverse voltage before recombination takes place. Thus, holes move towards the n - side and electrons towards the P - side - when the external circuit is made, the electrons flow through the external circuit and constitute the photo current.
(viii) When the incident light is zero, there exists a reverse current which is negligible. This reverse current in the absence of any. incident light is called dark current and is. due to the thermally generated minority carriers.

Wireline	Wireless
Wireline communication (point-point communication) uses mediums like wires, cables, and optical fibers.	Wireless communication uses free space as a communication medium.
These systems cannot be used for long-distance transmission they are connected physically.	The signals are transmitted in the form of electromagnetic waves with the help of a transmitting antenna Hence wireless communication is used for long-distance transmission
Examples are telephone, intercom, and cable TV.	Examples are mobile, radio or TV broadcasting, and satellite communication.
Wireline up to 100 meters	Wireless up to several thousand kilometers

It is the maximum distance between the source and the destination up to which the signal is received with sufficient strength.

(i) Voltage regulators
(ii) Peak clippers
(iii) Calibrating voltages

If the positive terminal battery is conneted to the n-side and the negative potential to the p-side, the junction is said to be reverse biased.

Band of very large number of closely spaced energy levels in a very small energy range is known as energy band.

\({ I }_{ B }=\frac { { V }_{ i } }{ { R }_{ B } } =\frac { 20V }{ 500k\Omega } =40\mu A\)  [∵ V_BE = 0V]
\({ I }_{ C }=\frac { { V }_{ CC } }{ { R }_{ C } } =\frac { 20V }{ 4k\Omega } =5mA\) [∵ V_CE = 0V]
\(\beta =\frac { { I }_{ C } }{ { I }_{ B } } =\frac { 5mA }{ 40\mu A } =125\)

\({ E }_{ g }=\frac { hc }{ \lambda } \)
Therefore,
\(\lambda =\frac { hc }{ { E }_{ g } } =\frac { 6.6\times { 10 }^{ -34 }\times 3\times { 10 }^{ 8 } }{ 1.875\times 1.6\times { 10 }^{ -19 } } \)
= 660 nm
The wavelength 660 nm corresponds to red colour light

The P.D. between A and B is given by
\(V =\left[V_{\mathrm{A}}-V_{\mathrm{B}}\right]-V_{\mathrm{b}}(\mathrm{Si}) \)
\(=[3.3-(-7.4)]-0.7 \)
\(=10.7-0.7=10 \mathrm{~V} \)
The value of current flowing through AB can be obtained by using Ohm’s law
\(I=\frac { V }{ R } =\frac { 10}{ 1\times { 10 }^{ 3 } } ={ 10 }^{ -2 }A=10mA\)

(i) The emitter-base junction is forward biased by a dc power supply Vm and the collector-based junction is reverse biased by the bias power supply V_cB
(ii) The forward bias across the emitter base junction causes the majority charge carriers electrons in the emitter region to flow towards the base region and constitutes the emitter current (I_E).
(iii) Since the base region is very narrow, most of the electrons reach the collector region.
(iv) The electrons that reach the collector region will be attracted by the collector terminal as it has positive potential and flows through the external circuit. This constitutes the collector current(I_c)
(v) The holes that are lost due to recombination in the base region ate replaced by the positive potential of the bias voltage V_EE and constitute the base current (I_B)
\( \mathrm{I}_{\mathrm{E}}=\mathrm{I}_{\mathrm{B}}+\mathrm{I}_{\mathrm{C}} \)
\(\mathrm{I}_{\mathrm{E}} \approx \mathrm{I}_{\mathrm{C}} \)     \((\because \mathrm{I}_{\mathrm{B}} is\ very\ small )\)

S.No	Avalanche breakdown	Zener breakdown
(i)	Heavily doped p-n junctions have narrow depletion layers of the order of <10-6 m.	It occurs in lightly doped junctions  Which have wide depletion layers.
(ii)	Electric field produced is strong in nature.	Weak electric field is produced.
(iii)	When a reverse voltage across the junction is increased to the breakdown limit, a very strong electric field is set up. It ruptures the covalent bonds in the lattice and thereby generating electronic-hole pairs. This effect is called Zener effect	Thermally generated minority charge carriers accelerated by the electric field gains sufficient kinetic energy, collide with the semiconductor atoms while passing through the depletion region. This leads to the breaking of covalent bonds and in turn covalent bonds and in turn generates electron-hole pairs
(iv)	Even a small further increases in reverse voltage produces a large number of charge carriers. Hence the junction has very low resistance in the breakdown region.	The newly generated charged carriers are also accelerated by the electric field resulting in more collisions and further production of charged carriers.
(v)	This process of emission of electrons due to the strong electric field is known as internal field emission or field ionization.	This cumulative process leads to an avalanche of charge carriers across the junction and consequently reduces the reverse resistance the diode current increases sharply.

The process of adding impurities to the instrinsic semiconductor is called doping.

S.No Intrinsic semiconductor Extrinsic semiconductor (i)  A semiconductor in its pure form without impurity is called an intrinsic
semiconductor. When small amount of impurity is doped in pure semiconductors it becomes extrinsic semiconductors.
  (ii) The number of free electrons in conduction band is almost equal to number of holes in valence band. The number of free electrons and holes is never equal. (iii) Electrical conductivity is a function of temperature along. Its electrical conductivity depends upon the temperature as well as on the quantity of impurity atoms doped the structure.

RADAR stands for RAdio Detection And Ranging.

(i) Radar basically stands for Radio Detection and Ranging System.
(ii) It is one of the important applications of communication systems' and is mainly used to sense, detect, and locate distant objects like aircraft, ships, spacecraft, etc.
(iii) The angle, range, or velocity of the objects that are invisible to the human eye can be determined.
(iii) Radar uses electromagnetic waves for communication. The electromagnetic signal is initially radiated into space by an antenna in all directions.
(iv) When this signal strikes the targeted object, it gets reflected or reradiated in many directions.
(v) This reflected (echo) signal is received by the radar antenna which in turn is delivered to the receiver.
(vi) Then, it is processed and amplified to determine the geographical statistics of the object. The range is determined by calculating the time taken by the signal to travel from RADAR to the target and back.
Applications :
Radars find extensive applications in almost all fields.
(i) In military, it is used for locating and detecting the targets.
(ii) It is used in navigation systems such as ship borne surface search, air search and weapons guidance systems.
(iii) To measure precipitation .rate and wind speed in meteorological observations, Radars are used.
(iv) It is employed to locate and rescue people in emergency situations.

α = 0.98
I_Cu = 0.6 μA
\(\alpha =\frac { \beta }{ 1+\beta } \)
(or)
\(0.98=\frac { 1 }{ \frac { 1 }{ \beta } +1 } \)
β = 49
I_CEO = (1 + β)I_CBO
= (1 + 49) x 0.6μA
I_CEO = 30 μA
= (1 + 49) x 0.6 μA
I_CEO = 30 μA
I_C = βI_B+ I_CEO
= 49 x 20 μA + 30 μA
I_C = 1.01 mA

Insulators:
(i) The valence band and the conduction band are separated by a large energy gap.
(ii) The forbidden energy gap is approximately 6 eV in insulators.
(iii) The gap is very large that electrons from valence band cannot move into conduction band even on the application of strong external electric field or the increase in temperature.
Metals
(i) In metals, the valence band and conduction band overlap.
(ii) Hence, electrons can move freely into the conduction band which results in a large number of free electrons in the conduction band.
Semiconductors
(i) In semiconductors, there exists a narrow forbidden energy gap (E < 3eV) between - g the valence band and the conduction band.
(ii) Free electrons are small in number, the conductivity of the semiconductors is not as high as that of the conductors.

(i) This gives the variation of collector current (I_C) with changes in base current (I_B) at constant collector-emitter voltage (V_CE).
(ii) It is seen that a small Ie flows even when I_B is zero. This current is called the common emitter leakage current (I_CEQ) which is due to the flow of minority charge carriers.
Forward current gain:
(i) The ratio of the change in collector current (ΔI_C) to the change in base current (ΔI_B) at constant collector-emitter voltage (V_CE) is called forward current gain(β)
\(\beta ={ \left( \frac { \triangle { I }_{ C } }{ \triangle { I }_{ B } } \right) }_{ { V }_{ CE } }\)
(ii) It is value is very high and it generally ranges from 50 to 200. It depends on the construction of the transistors and will be provided by the manufacturer.

Insulators
(i) The gap is very large that electrons from valence band cannot move into conduction band even on the application of strong external electric field or the increase in temperature.
(ii) The electrical conduction is not possible as the free electrons are almost nil.
(iii) Its resistivity is in the range of 10¹¹ - 10¹⁹ Ωm
Metals
(i) Conduction becomes possible even at low temperatures.
(ii) The application of electric field provides sufficient energy to the electrons to drift in a particular' direction to constitute a current.
(iii) The resistivity value lies between 10^-2 and 10^-8Ωm
Semiconductors
(i) At a finite temperature, thermal agitations in the solid can break the covalent bond between the atoms.
(ii) This releases some electrons from valence band to conduction band
(iii) The resistivity value of semiconductors is from 10^-5 to 10^-6 Ωm
(iv) When the temperature is increased further, more number of electrons is promoted to the conduction band and increases the conduction.
(v) Thus, electrical conduction increases with the increase in temperature.

(i) The transistor in saturation region acts as a closed switch while in cut-off region, it acts as an open switch.
(ii) It functions like an electronic switch that helps to turn ON or OFF a given circuit by a small control signal which keeps the transistor either in saturation region or in cut-off region.

When the input is low:
(i) When the input is low (say 0 V), the base current is zero and transistor is not properly forward biased.
(ii) It is in cut off region, As a result, the collector current is zero and correspondingly the voltage drop across R_C, also becomes nearly zero, The output voltage is high and Is equal to V_CC. 
(iii) It means that the no current flows through the transistor and it is said to be switched off. The transistor acts as an open switch.
When the input is high:
(i) When input voltage is increased to a certain high value (say +5 V), the base current (I_B) increases and in turn decreases the collector current to its maximum.
(ii) The transistor will move into the saturation region. The increase in collector current (I_C). increases the voltage drop across R_C, thereby thereby lowering the output voltage, close to zero (since V_o = V_CC -I_CR_C). It means that maximum current flows through the transistor and it is said to be switched on. 
(iii)The transistor acts as a closed switch.

HaIf wave rectifier:
Only one half of the input wave reaches the output. Therefore it is called half wave rectifier.
Construction:

(i) The circuit consists of a transformer, a p-n junction diode and a resistor
(ii) In a half wave rectifier circuit, either a positive half or the negative half of the AC input is passed through by the diode while the other half is blocked
(iii) It acts as a rectifier diode.

(iv) Efficiency (η) is the ratio of the output DC power to the AC input power circuit. supplied to the circuit.
(v) The efficiency (η) of a half wave rectifier is found to be 40.6 %.

i) AND gate
a) Circuit Symbol:
The circuit symbol of a two input AND gate is shown in Figure (a). A and B are inputs and Y is the output. It is a logic gate and hence A, B, and Y can have the value of either 1 or 0

Two input AND gate

Inputs		outputs
A	B	Y = A + B
0	0	0
0	1	0
1	0	0
1	1	1

Truth table
b) Boolean equation:
Y = A.B
It performs logical multiplication and is different from arithmetic multiplication.
c) Logic operation:
The output of AND gate is high only when all the inputs are high. In the rest of the cases, the output is low. It is represented in the truth table (Figure (b).
ii) OR gate
a) Circuit Symbol:
The circuit symbol of a two input OR gate is shown in Figure (a). A and B are inputs and Y is the output. 

The input OR gate

Inputs		outputs
A	B	Y = A + B
0	0	0
0	1	1
1	0	1
1	1	1

Truth table
a) Boolean equation:
A + B = Y
It performs logical addition and is different from arithmetic addition.
b) Logic operation:
The output of OR gate is high (logic 1 state) when either of the inputs or both are high. The truth table of OR gate is shown in Figure (a).
iii) NOT gate
a) Circuit Symbol:
The circuit symbol of NOT gate is shown in Figure (a). A and B are inputs and Y is the output. 

NOT gate

Inputs	Output
A	Y = Ā
0	1
1	0

Truth table
a) Boolean equation:
Y = Ā
b) Logic operation:
The output is the complement of the input. It is represented with an overbar. It is also called as inverter. The truth table infers that the output Y is I when input A is 0 and vice versa. The truth table of NOT is shown in Figure (b).
iv) NAND gate
a) Circuit Symbol:
The circuit symbol of NAND gate is shown in Figure (a). A and B are inputs and Y is the output.

Two input NAND gate

Inputs		Output (AND)	outputs (NAND)
A	B	Z = A.B	Y = \(\overline { A.B } \)
0	0	0	1
0	1	0	1
1	0	0	1
1	1	1	0

Truth table
b) Boolean equation:
Y = \(\overline { A.B } \)
Logic operation:
The output Y equals, the complement of AND operation. The circuit is an AND gate followed by a NOT gate. Therefore, it is summarized as NAND. The output is at logic zero only when all the inputs are high. The rest of the cases, the output is high (Logic I state). The truth table of NAND gate is shown in Figure (b).
v) NOR gate
a) Circuit Symbol:
The circuit symbol of NOR gate is shown in Figure (a). A and B are inputs and Y is the output.

Two input NANS gate

Inputs		Output (OR)	outputs (NOR)
A	B	Z = A + B	Y = \(\overline { A+B } \)
0	0	0	1
0	1	1	0
1	0	1	0
1	1	1	0

Truth table
Boolean equation:
Y =  \(\overline { A+B } \)
Logic operation:
The output Y equals the complement of OR operation (A OR B). The circuit is an OR gate followed by a NOT gate and is summarized as NOR. The output is high when all the inputs are low. The output is low for all other combinations of inputs. The truth table of NOR gate is shown in Figure (b).
vi) Ex-OR gate
a) Circuit Symbol:
The circuit symbol of Ex-OR gate is shown in Figure (a). A and B are inputs and Y is the output. The Ex-OR operation is denoted as ⊕

Ex-OR gate

Inputs		outputs (Ex-OR)
A	B	Y = A ⊕ B
0	0	0
0	1	1
1	0	1
1	1	0

Truth table
b) Boolean equation
Y =  \(A.\overline { B } \) + \(\overline { A }.B \)
Y = A ⊕ B
Logic operation: 
The output is high only when either of the two inputs is high. In the case of an Ex-OR gate with more than two inputs, the output will be high when odd number of inputs are high. The truth table of Ex-OR gate is shown in Figure (b).

Fiber optic communication:
(i) The method of transmitting information from one place to another in terms of light pulses through an optical fiber is called fiber optic communication. It works on the principle of total internal reflection.
Applications:
(ii) Optical fiber system has a number of applications namely, international communication, inter-city communication, data links, plant and traffic control and defense applications.
(iii) Fiber cables are very thin and weigh lesser than copper cables.
(iv) This system has much larger band width. This means that its information carrying capacity is larger.
(v) Fiber optic system is immune to electrical interferences.
(vi) Fiber optic cables are cheaper than copper cables.

(i) GPS stands for Global Positioning System. It is a global navigation satellite system that offers geolocation and time information to a GPS receiver anywhere on or near the Earth.
(ii) GPS system works the assistance of a satellite network.
(iii) Each of these satellites broadcasts a precise, signal and these signals convey the location data are received by a low-cost aerial which is then translated by the GPS software.
(iv) The software is able to recognize the satellite, its location, and the time taken by the signals to travel from each satellite.
(v) The software then processes the data it accepts from each satellite to estimate the location of the receiver.
Applications:
Global positioning system is highly useful in many fields such as fleet vehicle management (for tracking cars trucks and buses), wildlife management (for counting of wild animals), and engineering (for making tunnels, brides, etc).

a) Information (Baseband or input signal):
i) Information can be in the form of a sound signal like speech, music, pictures, or computer data which is given as input to the input transducer.
b) Input transducer:
i) It converts the information which is in the form of sound, music, pictures or computer data into corresponding electrical signals.
ii) The electrical equivalent of the original information is called the baseband signal.
iii) The best example is the microphone that converts sound energy into electrical energy.
c) Transmitter
i) It feeds the electrical signal from the transducer to the communication channel
ii) It consists of circuits such as amplifier, oscillator, modulator, and power amplifier.
iii) Amplifier: The transducer output is very weak and is amplified by the amplifier.
iv) Oscillator: It generates high-frequency carrier wave (a sinusoidal wave) for long distance transmission into space. As the energy of a wave is proportional to its frequency, the carrier wave has very high energy.
v) Modulator: It superimposes the baseband signal onto the carrier signal and generates the modulated signal.
vi) Power amplifier: It increases the power level of the electrical signal in order to cover a large distance.
d) Transmitting antenna:
i) It radiates the radio signal into space in all directions.
ii) It travels in the form of electromagnetic waves with the speed of light.
e) Communication channel:
Communication channel is used to carry the electrical signal from transmitter to receiver with less noise or distortion.
Example: Wires, cables, optical fibres in wireline communication and free space in wireless communication.
f) Receiver:
i) The signals that are transmitted through the communication medium are received with the help of a receiving antenna and are fed into the receiver.
ii) The receiver consists of electronic circuits like demodulator, amplifier, detector etc. The demodulator extracts the baseband signal from the carrier signal.
iii) Then the baseband signal is detected and amplified using amplifiers.
iv) Finally, it is fed to the output transducer.
g) Repeaters:
i) Repeaters are used to increase the range or distance through which the signals are sent.
ii) It is a combination of transmitter and receiver.
iii) The signals are received, amplified, and retransmitted with a carrier signal of different frequency to the destination.
iv) The best example is the communication satellite in space
h) Output transducer:
i) It converts the electrical signal back to its original form such as sound, music, pictures or data.
ii) Examples of output transducers are loudspeakers, picture tubes, computer monitor, etc